1. Field of the Invention
The present invention relates to a digitized data processing apparatus which edits and converts digitized data obtained by scanning a model shape to be used in the preparation of an NC (numerical control) working program.
2. Description of the Prior Art
Conventionally, for formation of a mold having a freely curved surface, a model having the same shape as the mold is previously formed and profiling of the model is performed with a profile working machine. To form male and female mold parts, however, inverted models are required which are formed of plaster and which are difficult to form with accuracy. Moreover, the profiling speed using the profile working machine is considerably low.
With the advent of NC machine tools, the advantages of NC machining in terms of speed and reproducing performance have become known and some attempts have therefore been made to apply NC techniques to the formation of molds. For example, a digitizer apparatus has been developed which scans the surface of a model shape with a stylus (i.e., a probe) to obtain digitized data denoting stylus coordinate values, and which edits and converts the digitized data to prepare an NC working program. However, the NC working program thus formed only enables a process of working with a tool having the same shape as the stylus. That is, the conventional profile working process is merely separated into two processes associated through the NC working program.
An improved digitized data processing apparatus has also been developed which is capable of converting digitized data to enable working with a tool having a shape which is different from that of the stylus, which is capable of extracting a part of the digitized data corresponding to a particular work portion, and which is capable of preparing an NC working program for an inverted shape from the digitized data obtained by measuring the model without utilizing the digitized data on the inverted model. The above digitized data processing apparatus can prepare, by computation, suitable digitized data which is equivalent to corresponding data obtained with a digitizer apparatus based on equalizing the shape of the stylus to that of the desired tool and restricting the scanning range.
FIG. 1 is a block diagram of an example of the prior art digitized data processing apparatus. Digitized data DD (hereinafter referred to as "digitized measurement data") is stored in a digitized data memory means 2 via a digitized data input means 1. The digitized measurement data DD is read out of the digitized data memory means 2 and input to a digitized data editing means 3 where it is edited in accordance with an editing instruction DS input from a digitized data editing instruction input means 4 to form digitized data DO representing a tool path for working a work piece (which data is hereinafter referred to as "digitized tool path data"). The digitized tool path data DO is stored in the digitized data memory means 2. The digitized tool path data DO is read out of the digitized data memory means 2 and input to a digitized data NC program conversion means 5. An NC working program is thereby prepared and output.
The above digitized data processing apparatus enables an inverting processing to be performed as one of the steps for editing the digitized measurement data. That is, it can obtain, from the digitized measurement data of one model, digitized tool path data for the model shape (hereinafter referred to as "normal shape") and digitized tool path data for a shape formed by inverting the model shape (hereinafter referred to as "inverted shape"). Examination of the size of a normal shape work piece formed on the basis of a normal shape NC working program prepared by converting the digitized tool path data for the normal shape is performed by comparison measurement using a three-dimensional measuring apparatus. However, examination of the size of an inverted shape work piece formed on the basis of an inverted shape NC working program prepared by converting digitized tool path data for the inverted shape cannot be performed since there is no inverted shape model.